1. Area of the Art
The invention relates to artificial firelogs which contain additives added to create a crackling sound that mimics the sounds produced during the burning of natural wood logs. The random crackling sound is most prominent in the early portion of the burn and weakens in intensity during the burn cycle similar to the performance of burning natural wood logs.
2. Description of the Prior Art
Synthetic fireplace logs are manufactured from a broad range of flammable cellulosic components in combination with a binder, and possibly other additives. Typical flammable cellulosic components include wood particles, pulp, shavings or chips, sawdust, ground bark, shredded paper or cardboard, waxed cardboard, charcoal powder, spagnum moss, and agricultural waste materials such as straw, bagasse, grass clippings, leaves, cotton linter, rice hulls, peanut or other nut shells and coffee grounds. The binder is typically a flammable wax such as paraffin wax or slack wax or flammable vegetable oils such as stearic and/or paimitic acid or other fatty acids or esters. However, numerous other combustible components are used or could be used. This list of materials is not intended to limit the composition of flammable artificial logs. Other additives may include chemicals designed to color or otherwise modify or retard the flame, add aroma or change the burning characteristics to more closely mimic the burning of natural logs.
A single artificial log, which weighs 5-6 pounds, is designed to burn unattended for about 3-4 hours. For comparison, a 5-6 pound oak log will burn for about 1/3 of that time. To get a comparable burning time, 3 logs of 5-6 pounds are generally burned at one time. Also, to sustain a 3-4 hour burn with the desired ambiance and flame intensity, it is often necessary to stir the natural log fire and turn over the logs to get a relatively uniform and intense burn.
Typical prior art artificial logs burn much more quietly than natural logs and do not duplicate the roar of burning natural logs. Also, as discussed below, natural logs exhibit loud snapping and popping, the snapping and popping arising from heating of moisture and sap which naturally exist in the log.
U.S. Pat. No. 5,868,804 issued Feb. 9, 1999 to Williams, et al. is directed to an artificial log having an additive consisting of 1) mustard, flax, cumin, or sesame seed, or a combination thereof, 2) hollow synthetic spheres, or 3) a combination of the seed component and the hollow synthetic spheres, to provide an audible crackling sound during burning of the logs. U.S. Pat. No. 5,118,539 to Sebby et al., shows artificial fire logs containing seeds found in bird food mix, particularly hemp, millet and sunflower seeds, to provide a popping sound. Williams claims that the sound produced by the seeds disclosed by Sebby et al are inadequate as well as short lived and do not adequately duplicate the sound of natural burning logs.
The '804 patent indicates that the preferred seed must have a shell with sufficient strength to withstand heat for a period of time and to then suddenly burst as a result of buildup of inner pressure from gases formed from the water and oils within the seed. Suitable seeds are seamless with a round or oval shape. According to Williams, the seeds used by Sebby tend to burn and prematurely rupture. Williams identifies only mustard, flax, cumin and sesame seed as meeting his criteria.
Alternatively, synthetic hollow spheres or granular material, such as glass, ceramic or plastic spheres have been used. Williams et al uses Z-light W-1300 or W1800 silica-alumina ceramic spheres manufactured by 3M. These spheres are alleged to have the ability to provide a crackling sound through the whole burning cycle, a characteristic not shown by the seeds. Williams finds that the seed generated sound does not last the full burning time of the artificial log.
Using a test log formulation, Williams reports that the W1800 ceramic spheres provided popping or "poof" sound for the whole burning cycle of 3.25 to 3.5 hrs. The sound from the mustard and sesame seeds lasted for 2 to 2.25 hrs.(approximately 60 to 65% of the burning cycle) while the flax and cumin seeds produced sound for only about 0.75-1.25 hr (approximately 20 to about 35% of the burning cycle). This is in comparison to the Sebby et al sunflower and millet seeds which Williams reported lasted 0.25-0.5 hr.
Natural burning logs generate a snapping, popping and crackling sound as the moisture and oils naturally occurring in the wood are heated, creating steam and vapor. This expanding steam and vapor causes the wood to crack creating the observed sounds. However, these sounds will not persist throughout the burning cycle. As the wood is heated by the surrounding flames, the vaporizable components are dissipated long before the natural log stops burning. As a result, the sounds start as the natural wood starts to burn, increases in a random, but persistent manner for a period of time followed by a tapering off of the frequency of the sound. The longevity, persistence and frequency of these sounds depends on the moisture and oil content of the natural wood and the density and hardness of the wood. However, in typical natural fire wood, the sounds persist for about one-half of the burning cycle.
The prior art compositions either have a very short lived popping sound or the sound persists for a significantly longer portion of the burning cycle, thus creating an unrealistic simulation of the burning of natural logs, or the sound is not of a quality or volume to simulate burning of natural logs. Therefore, there is a need for a synthetic log that more closely simulates the actual performance of burning natural logs.